The present invention relates to a metallic staple which can be used particularly but not exclusively to join continuous elements made of wood or the like for example to manufacture frames for paintings or the like.
For the joining of contiguous wood elements for the manufacture of frames, a system is currently used which consists in locking said elements in the required mutual position and in inserting therein, from the rear side, one or more shaped metallic staples.
The staples are inserted edgeways and penetrate in both elements simultaneously at their connecting line.
The staples currently in use are of various types, but those most commonly used are substantially related to three types of execution.
A first type has a central flat portion and two lateral corrugations which diverge with respect to one another in the direction of insertion.
This staple, which is provided with a cutting edge with a two-sided taper, produces an optimum traction between the wood strips, especially in hard and fibrous woods, but since the central part cuts the fibers of the wood obliquely and has a profile with a very small radius of curvature, deformations and accumulations of material are produced proximate to the joint.
This effect is negligible on frames having certain dimensions (by way of indication, a width in excess of 20 mm), but become evident on small frames made of softwood.
A second type of metallic staple has a V-shaped central part which opens slightly in the direction of insertion, two small lateral flaps and a cutting edge with a two-sided taper.
This type of staple, differently from the preceding one, penetrates in the wood longitudinally with respect to the fibers, but generates a traction between the two strips and at the joint, carrying material toward the inner part of the corner and leaving a small crack or split on the outer part.
This unwanted effect is irrelevant for softwood, in which the slight splitting of the wood fibers is negligible.
A third type of metallic staple has a V-shaped central part, two small lateral wings and a cutting edge which has a single-sided taper.
Said staple penetrates the wood longitudinally with respect to the fibers, producing, by virtue of the presence of the single-sided taper, the effect of moving the material toward the inside of the corner, generating the required traction.
The finish of the joint thus obtained is good, although it is less solid than that obtained with the previously described metallic staples.
The degree of sharpness affects the effectiveness of the joint.